English abstract

By analyzing ventilatory parameters and/or blood lactate concentration, registered during an incremental treadmill exercise test, two breakpoints, manifesting metabolic changes, can be determined. These are the aerobic and the anaerobic threshold. The thresholds delineate three intensity zones – the zones of moderate, high, and very high intensity. Despite the fact that the anaerobic threshold has long been routinely used in medicine and athletic performance diagnostics, there is still no scientific consensus on this phenomenon, its mechanisms and methods for its determination. Based on the premise that the metabolic changes in the origin of the gas exchange thresholds would manifest themselves concurrently in the alteration of thermodynamics, the principal hypothesis of this investigation was set forth: during an incremental treadmill exercise test, in controlled microclimatic conditions, at a certain intensity a nonlinear increase of body core temperature appears, that is significantly positively correlated with the changes in ventilatory parameters and that can, therefore, be used in the evaluation of the anaerobic threshold. The aims of this investigation were: to determine the existence of a temperature threshold that can be used to detect the anaerobic threshold by exploring the core body temperature dynamics during an incremental treadmill exercise test with fine gradation of intensity, and by comparing the temperature and gas exchange parameters registered during the test; to determine differences between gas exchange and temperature parameters registered during the graded exercise test; to test the relationship between core body temperature dynamics, gas exchange parameters and heart rate during graded exercise. The sample consisted of 32 males (18-40 yrs.), regularly physically active (practicing running activities for at least one year). The participants performed an incremental treadmill exercise test (with speed increments by 0,5 km/h every 30 sec). During the test, gas exchange parameters (VO2, VCO2, VE/VO2, VE/VCO2) and rectal temperature (approx. 8 cm from the anal sphincter) were recorded. The gas exchange thresholds were determined by the V-slope method.34,36,41 The temperature thresholds were assessed according to the curve models and instructions defined in this investigation. Based on the dynamics of subjects' core body temperature during the graded exercise test, three distinctive patterns were described. A high objectiveness of assessment was determined for the second (anaerobic) temperature threshold (Cronbach α=0,941), but not for the first temperature threshold (α=0,693). None of the thresholds showed a satisfactory test-retest reliability (ICC=0,18 and 0,23 for the first and second temperature threshold, respectively). A high correlation between the second temperature and second ventilatory threshold was found (r=0,74, p<0,001). There were no statistically significant differences between the average values of temperature (8,14±0,87 km/h and 13,44±1,69 km/h for the first and second temperature threshold, respectively) and gas exchange (8,35±1,28 km/h and 13,09±2,07 km/h, for the first and second ventilatory threshold, respectively) thresholds (p>0,05), although a trend of somewhat higher values of the second temperature threshold in comparison with the second ventilatory threshold was noted. A significant positive correlation between the body core temperature dynamics during the incremental test and some indices of the aerobic capacity (vmax, vAP, FSAP), and a high correlation between the anaerobic temperature threshold and relative VO2max and vmax (r=0,62 and 0,82, respectively, p<0,01) were found. The results confirm that during an incremental treadmill exercise test, in controlled microclimatic conditions, there is a core body temperature threshold, that is positively related with changes in gas exchange parameters and can be used as an index of the anaerobic threshold. The results obtained in this study can be used as a basis for development of a new method for anaerobic threshold detection by monitoring core body temperature during graded exercise. The relationship between core body temperature dynamics during graded exercise and aerobic capacity indices may be used to develop new methods for aerobic capacity evaluation, by measurement of core body temperature during submaximal exercise.